Examples of the invention relate to a method and apparatus for servicing an inkjet page-wide-array print head.
Inkjet printers eject liquid ink through multiple nozzles to form characters and graphics on a page. Print quality is dependent upon printer resolution and print head performance. Printing at a 300 dpi (“dots per inch”) resolution yields print quality comparable to 300 dpi laserjet printing.
To achieve reliable performance, the inkjet print head and inkjet processes are designed to precisely control inkjet output. By controlling the timing, placement and volume of inkjet output droplets, reliable, repeatable character performance and graphic performance is achieved.
A clogged nozzle adversely impacts the placement and volume of inkjet output droplets as the ink droplet may be deflected from its intended destination and less than all ink may escape the nozzle. A seldom used nozzle may get dried ink or contaminants lodged in its orifice. Hot and dry environmental conditions, for example, speed up the drying process and may cause nozzles to clog. Also, contaminants from the external environment or from the printing process may get lodged in a nozzle blocking an orifice. Such clogging may occur despite design efforts to minimize ink drying and maintain a clean print head environment.
Accordingly, there is an ongoing need to provide methods and apparatus for cleaning inkjet print heads.
Conventional inkjet print heads span less than one inch and are scanned across the page. To perform a print operation the print head is moved in one direction while the page is moved in a perpendicular direction. In effect, the print head scans the page while ejecting ink droplets to form the desired printout. When not in use the print head moves into a service area where the print head is cleaned then capped. As the print head moves into a rest position, it traverses an elastomeric wiper (e.g., nitrile rubber). The wiper wipes ink from the print head surface. Scrapers are then used in some embodiments to clean off the wipers.
A page-wide-array (“PWA”) print head spans an entire page width (e.g. 8.5 inches) and includes thousands of nozzles. The PWA print head thus has many more nozzles than the scanning-type print heads discussed above. The PWA print head is formed on an elongated printbar. The printbar typically is oriented orthogonally to the paper path. During operation, the printbar and PWA print head are fixed while a page is fed adjacent to the print head. The PWA print head prints one or more lines at a time as the page moves relative to the print head. This compares to the printing of multiple characters at a time as achieved by scanning-type print heads.
Depending on the printout characteristics, certain nozzles on a PWA print head may be exercised less than other nozzles. For example, a user may print most of the time using one inch margins, and on occasion use less than one inch margins. The nozzles in the one inch margin area thus get exercised less regularly, and may clog more readily. This characteristic of uneven nozzle exercise is less common for a scanning-type print head. Scanning print head nozzles that start out in the margin area subsequently move out of the margin area and get exercised as the print head scans the page width.
Thus, certain nozzles on a PWA print head are more prone to clogging than on a scanning-type print head. In general, the problem of drying ink is more pronounced for a PWA print head than for a scanning-type print head. Accordingly, there is a need for an effective cleaning methodology for PWA print heads.
One solution is to remove the printbar and clean the print head in a manner similar to the cleaning of scanning-type print heads. However, to maintain reliable, accurate printing, the printbar is fixed and precisely positioned. There are several mechanical attachments that have to be undone to remove the printbar. Thus, the process would be timely and require careful actions. Also, repeated insertion and removal may wear on the components used for precisely fixing the printbar adding play to the printbar. Thus, it is desirable to use a cleaning methodology for cleaning the print head while in place.
There are various prior solutions for the servicing of a print head which use a dedicated service station, but these typically involve the movement of a print head carriage to the service station. These solutions are not suitable for a PWA printer because they are not suitable for fixed print heads, which do not use a carriage. It is not appropriate to provide movement of the print head bar as a whole to travel to a service location, as this would require the printer footprint to be excessive.